Epoxy compounds are led to ring-opening polymers by a ring-opening reaction of an epoxide. For example, epoxy resins which are compounds having two or more epoxy groups in their molecules undergo a ring-opening reaction of an epoxide by the action of a curing catalyst to form a polymer having a three-dimensional structure. An amine type compound or Lewis acid is usually used as an epoxy resin curing catalyst.
In this ring-opening reaction of an epoxide, when a nucleophilic reagent such as an amine exists, an anion is produced and polymerizes an epoxy ring ionically. Also, in the case where, for example, an acid hydride is reacted with a tertiary amine to generate a carboxylate anion, this anion is reacted with an epoxy group to cause a curing of a resin. As mentioned above, an anionic polymerization process is involved in the ring-opening polymerization of an epoxy compound. The epoxy curing catalyst which induces anionic polymerization and has been conventionally used in general may be said to be one which induces a reaction with an epoxy group by forming the anion mentioned above.
As materials having such a reaction mechanism, for example, an imidazole catalyst type curing agent and the like are known, wherein an anion produced by a reaction between the curing agent and an epoxy group is supplied to a reaction with an epoxy group. On the other hand, an epoxy resin composition prepared by compounding an ion-containing polymer in an epoxy resin is disclosed (see, for example, Patent Document 1). In the above patent document, an ion-containing polymer is used as a curing agent in an epoxy resin to thereby obtain a cured product exhibiting very excellent heat resistance. However, the production of the ion-containing polymer is usually difficult and it is therefore difficult to obtain various polymers as the ion-containing polymers with ease. Also, the above composition uses an epoxy resin as the epoxy compound to thereby generate a crosslinked epoxy cured product.
The improvement of the physical property of a polymer of an epoxy compound relates to a theme which opens up the following possibilities. Specifically, if a polymer of monofunctional epoxy compound having a high degree of polymerization can be obtained, it is expected to be a polymer differing entirely in physical properties from conventional crosslinking type epoxy resins. Also, in the case of a polymer of a di- or more functional epoxy resin, it is expected to obtain a high-crosslinking density polymer without a scarcely crosslinked part and hence high uniformity. There are the possibilities that these epoxy polymers (means a ring-opening polymer of an epoxide, the same as follows) exhibit thermal plasticity or unique physical property in, for example, physical strength. Such a polymer may be said to comply with the demand in the technical field concerned in which it is demanded of epoxy resins to have more excellent physical property correlating with technical innovation in an industrial field.
Therefore, the inventors study concerning a novel anionic polymerization initiator that has not been tried to use it in conventional epoxy curing agents and curing promoters will realize the expectations for the possibility of easy production of a polymerization initiator, high polymerization reaction rate, a high degree of polymerization, attainment of an epoxy polymer having physical properties that have not been found in conventional epoxy polymers and an improvement in cured properties.
Patent Document 1: Publication of Japanese Patent Application Laid-Open (JP-A) No. 2004-204186.